Porphyrin distributions in lacustrine and marine shales as indicators of paleodepositional environments
Conference
·
OSTI ID:425812
- Univ. of New Orleans, LA (United States)
- Univ. of Bristol (United Kingdom)
Porphyrins, organic molecules derived from chlorophyll, were assessed as potential paleoenvironmental indicators (biomarkers) of oil shales. The differences between the porphyrins from shales and coals are well established. However, the more subtle differentiation between the porphyrin distribution patterns of the lacustrine and marine oil shales is not documented. The lacustrine shales studied here are from Tertiary fault basins in China. The Mesozoic marine oil shales came from a variety of geographic and stratigraphic settings. The bulk of porphyrins occurs in the carbon number range from C{sub 30} to C{sub 33}. The C{sub 32} porphyrin is the most abundant irrespective of shale origin. The acustrine shales contain porphyrins in the C{sub 28}-C{sub 35} range whereas the marine shales usually have porphyrins in the C{sub 25}-C{sub 36} range. The DPEP, ie., Class A-2 porphyrins are dominant both in lacustrine and marine shales. However, the DPEP ie., Class A-4 porphyrins are absent in lacustrine shales. Moreover, marine shales contain vanadyl porphyrins whereas lacustrine shales contain nickel porphyrins. Finally, the absolute amounts of posphyrins in lake sediments are much lower than in marine sediments. Differences amongst porphyrin characteristics of thermally immature organic-rich shales are only in part attributed to the great variety of their precursor molecules, i.e., chlorophylls. Most likely, the dominant control was exerted by the intensity of anoxia during early diagenesis.
- OSTI ID:
- 425812
- Report Number(s):
- CONF-960527--
- Country of Publication:
- United States
- Language:
- English
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